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  集合进阶(三)-(泛型)
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      <h2 id="一、泛型"><a href="#一、泛型" class="headerlink" title="一、泛型"></a>一、泛型</h2><h3 id="概述"><a href="#概述" class="headerlink" title="概述"></a>概述</h3><p><strong>泛型</strong>：是JDK5中引入的特性，它提供了编译时类型安全检测机制，该机制允许在编译时检测到非法的类型</p>
<p>本质是<strong>参数化类型</strong>，也就是说所操作的数据类型被指定为一个参数</p>
<p><strong>参数化类型</strong>就是<strong>将类型由原来的具体的类型参数化，然后在使用/调用时传入具体的类型</strong>。这种参数类型可以用在类、方法和接口中，分别被称为泛型类、泛型方法、泛型接口</p>
<h3 id="定义格式"><a href="#定义格式" class="headerlink" title="定义格式"></a>定义格式</h3><ul>
<li>&lt;类型&gt;：指定一种类型的格式。这里的类型可以看成是形参</li>
<li>&lt;类型1，类型2…&gt;:指定多种类型的格式，多种类型之间用逗号隔开。这里的类型可以看成是形参</li>
<li>将来具体调用时候给定的类型可以看成是实参，并且实参的类型只能是引用数据类型</li>
</ul>
<h3 id="泛型的好处"><a href="#泛型的好处" class="headerlink" title="泛型的好处"></a>泛型的好处</h3><ul>
<li>把运行时期的问题提前到编译期间</li>
<li>避免了强制类型转换</li>
</ul>
<a id="more"></a>
<h3 id="泛型类"><a href="#泛型类" class="headerlink" title="泛型类"></a>泛型类</h3><p>泛型类的定义格式：</p>
<ul>
<li>格式：修饰符 class 类名&lt;类型&gt;{ }</li>
<li>范例：public class Generic<T>{ }</li>
</ul>
<p>常见的如<strong>T、E、K、V</strong>等形式的参数常用于表示泛型</p>
<p><img src="https://yolin121.oss-cn-beijing.aliyuncs.com/blogimg/Snipaste_2020-07-29_13-03-57.jpg" alt=""></p>
<h3 id="泛型方法"><a href="#泛型方法" class="headerlink" title="泛型方法"></a>泛型方法</h3><p>首先我们知道可以通过下面的方式使用泛型：</p>
<p><img src="https://yolin121.oss-cn-beijing.aliyuncs.com/blogimg/Snipaste_2020-07-29_13-24-11.jpg" alt=""></p>
<p>每次创建对象时都要确定数据类型，这样会显得很麻烦，解决这一问题就要用到泛型方法</p>
<p><strong>定义格式</strong></p>
<ul>
<li>格式：修饰符&lt;类型&gt; 返回值类型 方法名(类型 变量名)</li>
<li>范例<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> &lt;T&gt; <span class="function"><span class="keyword">void</span> <span class="title">show</span><span class="params">(T t)</span></span>&#123; &#125;</span><br></pre></td></tr></table></figure>

</li>
</ul>
<p>于是就有了下面的简单方法</p>
<p><img src="https://yolin121.oss-cn-beijing.aliyuncs.com/blogimg/Snipaste_2020-07-29_13-36-37.jpg" alt=""></p>
<h3 id="泛型接口"><a href="#泛型接口" class="headerlink" title="泛型接口"></a>泛型接口</h3><p><strong>定义格式</strong></p>
<ul>
<li>格式： 修饰符 interface 接口名&lt;类型&gt;{ }</li>
<li>范例：<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">interface</span> <span class="title">Generic</span>&lt;<span class="title">T</span>&gt;</span>&#123; &#125;</span><br></pre></td></tr></table></figure>

</li>
</ul>
<p><img src="https://yolin121.oss-cn-beijing.aliyuncs.com/blogimg/Snipaste_2020-07-29_19-11-18.jpg" alt=""></p>
<h2 id="二、可变参数"><a href="#二、可变参数" class="headerlink" title="二、可变参数"></a>二、可变参数</h2><p>先来开一段代码</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">demo</span></span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span></span>&#123;</span><br><span class="line">        System.out.println(sum(<span class="number">10</span>,<span class="number">20</span>));</span><br><span class="line">        System.out.println(sum(<span class="number">10</span>,<span class="number">20</span>,<span class="number">30</span>));</span><br><span class="line">        System.out.println(sum(<span class="number">10</span>,<span class="number">20</span>,<span class="number">30</span>,<span class="number">40</span>);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">int</span> <span class="title">sum</span><span class="params">(<span class="keyword">int</span> a,<span class="keyword">int</span> b)</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> a+b;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">int</span> <span class="title">sum</span><span class="params">(<span class="keyword">int</span> a,<span class="keyword">int</span> b,<span class="keyword">int</span> c)</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> a+b+c;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">int</span> <span class="title">sum</span><span class="params">(<span class="keyword">int</span> a,<span class="keyword">int</span> b,<span class="keyword">int</span> c,<span class="keyword">int</span> d)</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> a+b+c+d;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>当参数不一时需要写特定的带参方法，这样就很麻烦，所以就要引入可变参数</p>
<h3 id="可变参数"><a href="#可变参数" class="headerlink" title="可变参数"></a>可变参数</h3><p>可变参数又称参数个数可变，用作方法的形参出现，那么方法参数个数就是可变的了</p>
<ul>
<li>格式： 修饰符 返回值类型 方法名(数据类型···a){ }</li>
<li>范例：<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">int</span> <span class="title">sum</span><span class="params">(<span class="keyword">int</span>···a)</span></span>&#123; &#125;</span><br></pre></td></tr></table></figure>

</li>
</ul>
<p><img src="https://yolin121.oss-cn-beijing.aliyuncs.com/blogimg/Snipaste_2020-07-29_20-21-30.jpg" alt=""></p>
<p>注意事项：</p>
<ul>
<li>这里的变量（a）实际是个数组</li>
<li>如果一个方法有多个参数，包含可变参数，<strong>可变参数要放在最后</strong><br><img src="https://yolin121.oss-cn-beijing.aliyuncs.com/blogimg/Snipaste_2020-07-29_20-39-58.jpg" alt=""></li>
</ul>
<h3 id="可变参数的使用"><a href="#可变参数的使用" class="headerlink" title="可变参数的使用"></a>可变参数的使用</h3><p>Arrays工具类中有一个静态方法：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">&#x2F;&#x2F;返回由指定数组支持的固定大小的列表</span><br><span class="line">public static &lt;T&gt; List&lt;T&gt; asList(T... a)</span><br><span class="line">&#x2F;&#x2F;返回的集合不能做增删操作，可以做修改操作</span><br></pre></td></tr></table></figure>

<p><img src="https://yolin121.oss-cn-beijing.aliyuncs.com/blogimg/Snipaste_2020-07-29_22-31-07.jpg" alt=""></p>
<p>List接口中有一个静态方法：</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//返回包含任意数量元素的不可变列表</span></span><br><span class="line"><span class="keyword">public</span> <span class="keyword">static</span> &lt;E&gt; <span class="function">List&lt;E&gt; <span class="title">of</span><span class="params">(E... elements)</span></span></span><br><span class="line"><span class="function"><span class="comment">//返回的集合不能做增删改操作</span></span></span><br></pre></td></tr></table></figure>


<p>Set接口中有个静态方法：</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//返回一个包含任意数量元素的不可变集合</span></span><br><span class="line"><span class="keyword">public</span> <span class="keyword">static</span> &lt;E&gt; <span class="function">Set&lt;E&gt; <span class="title">of</span><span class="params">(E... elements)</span></span></span><br><span class="line"><span class="function"><span class="comment">//返回的集合不能做增删操作，没有修改的方法</span></span></span><br></pre></td></tr></table></figure>


      
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            <div class="pswp__share-modal pswp__share-modal--hidden pswp__single-tap">
                <div class="pswp__share-tooltip"></div>
            </div>

            <button class="pswp__button pswp__button--arrow--left" title="Previous (arrow left)">
            </button>

            <button class="pswp__button pswp__button--arrow--right" title="Next (arrow right)">
            </button>

            <div class="pswp__caption">
                <div class="pswp__caption__center"></div>
            </div>

        </div>

    </div>

</div>

<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/photoswipe@4.1.3/dist/photoswipe.min.css">
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/photoswipe@4.1.3/dist/default-skin/default-skin.css">
<script src="https://cdn.jsdelivr.net/npm/photoswipe@4.1.3/dist/photoswipe.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/photoswipe@4.1.3/dist/photoswipe-ui-default.min.js"></script>

<script>
    function viewer_init() {
        let pswpElement = document.querySelectorAll('.pswp')[0];
        let $imgArr = document.querySelectorAll(('.article-entry img:not(.reward-img)'))

        $imgArr.forEach(($em, i) => {
            $em.onclick = () => {
                // slider展开状态
                // todo: 这样不好，后面改成状态
                if (document.querySelector('.left-col.show')) return
                let items = []
                $imgArr.forEach(($em2, i2) => {
                    let img = $em2.getAttribute('data-idx', i2)
                    let src = $em2.getAttribute('data-target') || $em2.getAttribute('src')
                    let title = $em2.getAttribute('alt')
                    // 获得原图尺寸
                    const image = new Image()
                    image.src = src
                    items.push({
                        src: src,
                        w: image.width || $em2.width,
                        h: image.height || $em2.height,
                        title: title
                    })
                })
                var gallery = new PhotoSwipe(pswpElement, PhotoSwipeUI_Default, items, {
                    index: parseInt(i)
                });
                gallery.init()
            }
        })
    }
    viewer_init()
</script>



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